Ceramic arcing plate material



Dec. 16, 1958 A. E. STRINGFELLOW 2,864,919

CERAMIC ARCING PLATE MATERIAL Filed May ll, 1955 g l v) Vf \l WEA WMV M V 2,864,919 y Patented Dec. 16, 1958 2 percent SiOz. Preferably a more limited composition` range may be included, which will contain a minimum of fty percent cordierite` crystals and have an ultimate analysis consisting essentially of to 13 percent of MgO,

CERAMIC ARCING PLATE MATERIAL 5 37 to 57 percent A1203 and 38 to 50 percent of Si02.

Accordingly it isl an object of my invention to provide Ale, cgmlgfeuow Haddoneld J" aslgnor to as a novel ceramic arcing material a composition containircult Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania ing a substantial quantity of cordierite crystals and havmg an.ult1matecompos1tion consisting essentially of spe- Application May 11, 1955, Serial No. 507,632 10 ciiic proportions -of MgO, A1203 and Si02.

It is another object of ymy invention to provide a novel 2 Claims' (CL 20o-144) Cerami-c arcing plate Which will have outstanding interrupting ability, little loss in strength after interruptionv and be subject to very little deterioration andv erosion from My invention relates to a novel ceramic composition repeated use. to be used as the arc extinguishing means in connection lIt is still another object of my invention to provide a with circuit interrupting equipment, and to arcing plates novel method for preparing a cordierite-containing Ceand an arc chute embodying this novel composition. ramic composition which will be suitable for use ask a Circuit interruptingV equipment, asV is well known in ceramic arcing plate or assembly of such plates in circuit the art must have arc extinguishing means in order to cool interrupting equipment. off and deionize the arc which is formed between the These and other objects of my invention will become movable interrupting contacts. more apparent when taken in connection with the descrip- For relatively low voltage application, the arc extintion and the drawings in which: guishing means comprises a plurality of metallic mem- Figure 1 shows the three (3) component diagram bers which, through their high heat conductivity, are used Mg0-Al203-Si02 and having a portion thereof outto cool the arc and to prevent restriking thereof. Howlined to show the specific ceramic composition which I ever, for high voltage circuit interrupting equipment, for have -found particularly suitable in my ceramic arcing which my invention is directed, it is necessary to use inplates, and another small portion thereof outlined to sulating plates which are interleaved so as to provide a point out a particularly preferred embodiment of my intortuous path for the arc and thereby more rapidly eX- vention. The diagram is based on Weight percentages of tinguish the same. the three componentsand also indicates the point at which A typical arrangement for such plates is disclosed in cordierite, 2Mg0'2Al203-5Si02 as well as other comcopending applications (C-233) Serial No. 322,027, novil pounds containing these components will occur. By U. S. Patent No. 2,759,093, and (C-248) Serial No. dotted lines, compatability triangles are also outlined. 353,281 which are owned by applicants assignee, An- Figure Zillustrates a typical ceramic arcing plate which other arrangement which may be used is exemplified in may be made from my novel composition so that they my copending application (C-293) Serial No. 439,118. would form what is known as an arc chute The plates The ceramic insulating plates which have been used in as they appear in Figure 2 may be held in spaced-apart such are extinguishers in the past have comprised such relationship by independent spacer means as shown in materials as Transite, coldmolded asbestos, glass bonded 40 cop-ending application (C-248) Serial No. 353,281 or may mica and Zircon. be integral as shown in my copending application (C-293) The requirements for insulating plates of this type are Serial No. 439,118. such that they must befof a high dielectric strength having Moreover, the plates may be flat or flanged as indihigh resistance to thermal shock and must maintain their cated in these respective copending applications. strength before and after interruption and not be sub- Referring now to Figure 1, the novel composition. ject to deterioration and erosion from repeated contact which 1 propose to use in the ceramic arcing plates is with high voltage arcs. bounded by the percentages, 5 to 15 percent MgO, 22 to Some of the faults of the above mentioned materials 58 percent A1203 to 38 and 63 percent Si02. This entire are evident from the tabulation below. region is noted as area A and bounded by solid lines.

Strength Strength Interrupting Deterioratlon, Material Before After Ability Erosion, ete.

Interruption Interruption Transita Fair Poor Poor Extreme. Cold Molded Asbestos--. do do do Do. Glass Bonded Mica Very Good-- 43% Loss.- Fair Very High. Zircon Good swim, Loss-.. very oood- {gf)yEb-rne I propose to overcome these faults as well as other 60 it includes the area B hereinafter referred to. These disadvantages in the ceramic arcing materials known to compositions have been found to provide arcing plates theprior art by providing an arcing plate made of a novel having very high heat shock resistance, low strength loss ceramic composition which will have outstanding interunder interrupting conditions (0 to 10 percent after fty rupting ability, low strength loss during interruption and short circuits) and very good interrupting ability. will incur very little deterioration through repeated con- The composition which l particularly prefer and which tact with high voltage arcs. l have found that a plate gives the best quality fro-m all points considering intermeeting these requirements may be made from a comporupting ability, strength and ease of manufacture is sition containinga substantial quantity of cordierite crysbounded by the following coordinates of the phase diatals, specifically more than 50 percent of such crystals, gram: having a specific ultimate composition which can be de- 5 to 13 percent Mg0 fined on the Mg0-Si02--Al203 phase diagram as 5 to l5 percent MgO, 22 to 58 percent A1203 and 38 to 63 37 to 57 percent A1203 38 to 50 percent Si02 This area is indicated in Figure 1 as area B and is outlined by the cross-hatched lines. This area is characterized by compositions `having very low shrinkage values (between 0.6 and 2 percent), which makes the element easy to manufacture and relatively free from firing warpage, camber and cracks. These compositions give very high heat shock values and have high strength in the range of 10,000 to 11,000 p. s. i., which after 50 interruptions does not lower more than 2 to 5 percent of their initial strength. After this number of interruptions, arcing plates of this composition, although posibly havinga lower initial `strength than glass bonded mica arel found to have strengths equal or better than this or other high strength materials of the prior art.

In the weight percent triaxial diagram of Figure 1, the various phases which may occur are shown and compatability triangles connecting the indicated phases are outlined by the dotted lines.

vCordierite bodies are represented by a predominance of the compound 2MgO-2Al2O35SiO2 which is the composition of the cordierite crystal. They have an orthorhombic crystalline structure and are particularly important in my composition because of their very low co eicients of thermal expansion and their ability to withstand thermal shock. These cordierite crystals which appear in substantial amounts in my composition and preferably in amounts over 50 percent have been found to have a coeicient of thermal expansion of 3 l06 or less for the range of 60 to 1110L7 F. The formation of the cordierite in a ceramic body in the ternary system MgO--Al2O3-Si02 occurs to a greater or lesser extent over a rather wide compositional area and varies radically with the firing temperature.

In order to produce the cordierite crystals, the range of temperatures which I prefer to use varies from about 2300 to 2700" F. dependent upon the composition of the body and the raw materials used. Increases in ring temperatures causes an increase in individual crystal size. However, temperatures which are too high cause the cordierite to dissociate into mullite and a low viscosity melt.

The following specific Examples A, B and C cover the most desirable range of properties of starting mate rials which are used in the formation of my ceramic composition A B C Percent 35. 36. 1 28. 9

Percent Percent Sierramic Tale 25 Edgar Plastic Kaoli.n A-lO Alumina These materials are further described as follows: I. Sierramic Talc is a product of the Sierra Tale and Clay Company and commonly has the following analysis:

Percent SiO; 59. 62 MgO. 29. 91

NazO i Loss on ignition Percent T102. Loss on ignition III. A-10 Alumina is a product of the Aluminum Company of America and commonly has the following analysis:

Percent A1203 99. 68 SiO 0. 04 Misc. 0. 28

Oxide Composition i Percent MgO 11.5 11.5 8.5 AlzOa..-" 47. 0 41.0 44. 0 SiO: 41.5 47. 5 47. 5

From the examples above it can be seen that I particularly prefer that the starting composition falling within the cross-hatched area of Figure 1 should contain the following:

To illustrate a specific embodiment of the method for forming the cordierite crystals the following procedure is employed:

The raw clays are blended in a Simpson Mix-Muller with 4 percent water and 4 percent binder. The binder may be any of the commonly known organic binders which have long been used in the iiring of ceramic objects. Binders of this type are temporary in that they are either partially or completely burned out of the body upon firing. An example of a suitable binder would be a hemi-cellulose extract such as that going under the trade name Masonoid Another example would be methyl cellulose (see Pat. No. 2,358,407). This blend is screened through a 50 mesh screen to give additional mixing and break up any lumps. The blend is then compressed at 10,000 p. s. i. and then tired at 2534u F.

Figure 2 illustrates a ceramic arcing plate made of my novel composition and illustrates how the individual plates may be interleaved. The ceramic plate illustrated therein contains a notch cut vertically through the plate and arranged on one side of the vertical center line of the plate. Thus, the plate is divided into a Wider segment 11 and a narrower segment 12. These plates are resiliently mounted in the circuit interruptor and are interleaved so that the segments would appear alternately when viewing either the right or left hand side of the stack. Thus an arc must follow an elongated meanderling path in order to pass through a stack of interleaved These dielectric plates, so arranged, provide what is known as an arc chute The dotted lines in Figure 1 are indicative of changes in phase. In other words any point lying within an area defined by the dotted lines will contain a composition having phase mixtures of the compounds noted by the apices of the triangles defined by these dotted lines.

As previously mentioned and pointed out in the copending applications hereinbefore referred to, these arcing plates may be flat as shown or strengthened, spaced and supported by providing them with ribs or anges adjacent to each of the elongated sides of the plates and extending along substantially the full length of each side, in the manner set forth in my copending application Serial No. 439,118. The flanges may be one or both surfaces of the plate depending on whether an I-shaped or U-shaped cross-section is desired.

Although Figure 2 illustrates the staggered interleaved relationship of the plates it is clear thatit is within the scope and the spirit of my invention to include an assembly which contains any feasible number of plates so shown. The arrangement of plates, however, should provide the necessary tortuous path for the arc.

plates.

Arc chutes containing a plate assembly in which the plates have been composed of my novel ceramic composition have been shown, through various tests, to be superior to plates made of materials used in the prior art. For example, interruption tests on high voltage breakers have proven that plates of my novel composition have increased the interrupting rating over 90 percent over glass bonded mica and even more over the Transite type plates.

Moreover, the cordierite arcing material of the type herein disclosed and claimed have been found to give much better results under spalling tests. Apparently, my cordierite plates cool and heat more evenly so that less of a temperature gradient is set up during the arc extinguishing process thereby preventing variations in the coeicient of thermal expansion between the surface layer and the inner portion of the body which have often been found great enough to shear off the surface layer and thus result in spalling.

I do not intend to limit the scope of my invention to the specic type of arcing plates herein disclosed. It should be clear to those skilled in the art that my novel ceramic composition is suitable for use in various types of electrical insulators which come in contact wtih high voltage arcs. These would include arc plates, tube for load switches, rods for load switches, tubes for air blast switches, arc chute liner plates, arc chute cooling plates and arc plate spacers.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to Ibe bound not by the specic disclosure herein, but only by the appending claims.

I claim: l

1. In a circuit interrupter arc chute, a plurality of ceramic arcing plates having a low coefficient of thermal expansion and high heat shock resistance after repeated circuit interruptions, means for supporting and maintaining said plates in an interleaved, spaced-apart relationship so that an arc must follow an elongated path to pass through a stack of said plates, said plates being composed of a ceramic material consisting essentially of 5 to 13 percent MgO, 37 to 57 percent A1203 and 38 to percent SiO2 and containing more than 50 percent cordierite crystals.

2. In va circuit interrupter arc chute, a plurality of ceramic arcing plates having a low coefficient of thermal expansion and high'heat shock resistance after repeatedcircuit interruptions, means for supporting and maintaining said plates in an interleaved, spaced-apart relationship so that an arc must follow an elongated path to pass through a stack of said plates, said plates being composed of a ceramic material consisting essentially of 8.5 to 11.5 percent MgO, 41 to 47 percent A1203 and 41.5 to 47.5 percent Si02 and containing more thanv 50 percent cordierite crystals.

References Cited in the le of this patent UNITED STATES PATENTS 2,036,190 Benner et al. Apr. 7, 1936 FOREIGN PATENTS 109,919 Australia 1940 OTHER REFERENCES Journal of the American Ceramic Society, vol. 30, 1947, part II, page 79. 

1. IN A CIRCUIT INTERRUPTER ARC CHUTE A PLURATY OF CERAMIC ARCING PLATES HAVING A LOW COEFFIENCT TO THERMAL EXPANSION AND HIGH HEAT SHOCK RESISTANE AFTER REPAATED CIRCUIT INTERRUPTIONS MEANS FOR SUPPORTING AND MAINTAINI G SAID PLATES IN AN INTERLEAVED, SPACED-APART RELATIONSHIPSO THAT AN ARC MUST FOLLOW AN ELONGED PATH TO PASS THROUGH A STOCK OF SAID PLATES, SAID PLATES BEING COMPOSED OF A CERMIC MEATERIAL CONSISTING ESSENTIALLY OF 2 TO 13 PERCENT MGO, 37 TO 57 PERCENT AL233 AMD 38 TO 50 PERCENT SIO2 AD CONTAIMING MORE YHAN 50 PERCENT CORDINATE CRYSTALS. 